The present invention relates to position control systems. More specifically, the present invention relates to position control systems for vehicles on a fixed path.
Currently, the monitoring of vehicle motion along a path, such as a railway or a track, is carried out using a central controller or computer. The computer monitors each vehicle's position on the track and when vehicle spacing is within a predetermined minimum distance, all vehicles on the track are stopped. Such a system, in addition to the computer, includes multiple sensors mounted at various locations along the track and complex wiring for connecting each sensor and the computer.
For example, U.S. Pat. No. 4,864,306 describes a system in which machine readable trackside markers such as bar code markers are utilized along the track and are read by apparatus on board the train to provide track number identification, milepost identification and train direction. On board the train is equipment to provide train identification and train speed. This information is transmitted through transponders between trains and to a central station and is processed by apparatus on board the respective trains and the central location to provide visual and audible signals indicative of a potential train collision.
More recently, U.S. Pat. No. 7,182,298 describes a track network incorporating at least one node at which at least two track sections of the track network adjoin one another and also comprising a plurality of vehicles traveling along the track network and each of which comprises a control unit wherein the control of the movements of these vehicles can be effected and wherein the information relating to the successor or the forerunner vehicle is stored in the control unit of the vehicle and is updated when the vehicle passes a node of the track network.
However, because of the necessary computer, complex wiring, and multiple sensors, the system is difficult to integrate and to costly to maintain. Other disadvantages include the requirement to test and prove system functionality after track installation, the technical challenge of aligning a sensor and target for the vehicle to track interface, the inability to sense a spacing problem until it has become sufficiently severe to violate the minimum spacing, the inability to change spacing criteria without adding additional sensors which makes the system less flexible, and the inability to account for horizontal wheel slip and wheel and tire breakdown.
Therefore, to date, no suitable method or system for position control for a vehicle on a fixed track exists.